Graphene is in the form of a two-dimensional crystal of carbon atoms and great attention has been focused on graphene as industrial material since its discovery in 2004. Graphene has excellent electric, thermal, optical, and mechanical characteristics, and there are growing expectations for its applications in wide areas such as production of battery materials, energy storage materials, electronic devices, and composite materials.
Methods available for the production of graphene include the mechanical exfoliation method, CVD (chemical vapor deposition) method, and CEG (crystal epitaxial growth) method. Among others, the oxidization-and-reduction method, in which graphite oxide, also called oxidized black lead, is produced first through oxidization of natural graphite, followed by converting it into graphene through reduction reaction, is now expected as a promising industrial method for large-scale production.
In Patent document 1, graphite oxide is expanded and exfoliated while it is heated for reduction in order to produce thin flakes of graphite with a large specific surface area.
In Patent document 2, graphene is chemically reduced in the presence of catechol and subsequently freeze-dried to prepare a graphene powder with high dispersibility.
In Patent document 3, graphene oxide is chemically reduced in the presence of a water-soluble compound having a 9,9-bis-(substituted aryl)-fluorene backbone and the resulting aqueous graphene dispersion is mixed with an organic solvent. Then, graphene is recovered by centrifugal sedimentation and an organic solvent is added to prepare a graphene dispersion.
Non-patent document 1 reports that when the hydrazine reduction reaction of a thin graphite oxide film is prolonged, a high-degree reduction of acidic groups can be achieved to ensure an increase in the absorbance at 270 nm.